Measurement of the angular distribution of γ-rays after neutron capture by 139La for a T-violation search

Parity violating effects enhanced by up to 106 times compared to proton-proton scattering have been observed in several neutron capture induced compound nuclei. This enhancement is explained as an interference between an s-wave and a p-wave amplitude (s-p mixing). Theory predicts that this mechanism can also enhance T-violating effects. For estimation of this enhancement in a promising candidate nucleus, we measured the angular distribution of γ-rays in the (n,γ) reaction induced in a 139La target. Experiments were performed at J-PARC, using a germanium detector array at an intense neutron beam. Analysis of the observed angular dependence around the 0.74 eV p-wave resonance allowed us to determine the ratio of the partial p-wave neutron width to the total neutron width in the entrance channel of the compound nucleus. We also report our development of a 3He spin filter needed as an epithermal-neutron polarizer for the T-violation search.

A Method of Correction for Unresolved Levels in Fissile Nuclei

A method of correcting for unresolved levels in fissile nuclei is described. The method is based on the distribution of the ratio of the reduced neutron width to the total width of a level. Calculations are carried out on three sets of data for 233U, and it is shown that approximately one-quarter of the resonance levels are undetected.